The present invention relates to a drum brake assembly and in particular to a drum brake assembly that employs a single piece brake shoe.
A drum brake assembly of that kind is disclosed in Applicant's U.S. Pat. No. 5,246,093. That patent discloses a friction lined brake shoe which is of generally circular loop form and which defines two separate and opposed ends. The patent further discloses a drum brake assembly, in which an actuator is disposed between the opposed ends of the brake shoe for increasing the separation of the ends during a brake application to thereby radially expand the shoe to an operative condition, in which the friction lining engages the drum braking surface. The brake shoe is constructed to resiliently distort during radial expansion and to act as a return spring when the actuating force between the opposed ends is released, to return the shoe to a radially contracted, inoperative condition, in which the friction lining is spaced from the drum braking surface.
The drum brake assembly disclosed in U.S. Pat. No. 5,246,093 advantageously reduces the number of brake components compared to prior art drum brake assemblies and it simplifies machining or grinding of the friction lining during brake shoe manufacture. The reduction in components achieved in the drum brake assembly of U.S. Pat. No. 5,246,093 includes a reduction in the number of components employed to secure the brake shoe in place against the backing plate and within the drum, and therefore, compared to prior art drum brake assemblies, the brake shoe of U.S. Pat. No. 5,246,093 is less constrained within the drum brake assembly. In that assembly, the brake shoe is not fully restrained against “floating” or shifting movement (hereinafter referred to as “lateral movement”) across the backing plate when the drum brake assembly is in the inoperative condition. The brake shoe is not loose within the drum, as it is connected at the opposed shoe ends to the actuator and it is restrained against lifting away from the backing plate by spring clips or a conventional hold down spring, but those connections cannot under all circumstances, prevent the lateral movement referred to above. Thus, the brake shoe can, under certain circumstances, such as during excessive vibration, move laterally over the backing plate and that can cause the brake shoe to become misaligned within the drum when the drum brake assembly is in an inoperative condition, i.e., when there is no brake actuating load being applied, so as to reduce the running clearance between the friction lining and the drum braking surface below the set running clearance. In some circumstances, that misalignment may cause the brake shoe to engage the drum braking surface in the inoperative condition, which is undesirable.
It is an object of the invention to provide an improved brake assembly which employs a single piece brake shoe of the above described kind, in which the brake shoe is more reliably returned to a position spaced from contact with the drum braking surface in the inoperative condition.